Cks proteins belong to the new family of domain swapping proteins, that include several other interwined and dimeric protein structures in which the new assembly is essential for their function. Gel filtration experiments performed with these Cks molecules in presence of the CDK2 kinase clearly reinforces this hypothesis. We wish to determine with SR, the first structure between the CDK2 kinase and one of its important partner during cell cycle progression, CksHs1.